The invention relates to a test device for vehicles having a wheel rotation speed sensor which is sensitive to magnetic fields.
Such sensors are in use, for example, as Hall sensors or inductive sensors. The latter, for example, include a bar magnet which is arranged such that it cannot move. The bar magnet has a soft-magnetic pole pin which is fitted with an induction coil. The inductive sensors also include a toothed wheel which is coupled to the wheel rotation. The toothed wheel influences the magnetic fields. The toothed wheel rotates in front of the pole pin and, consequently, induces in the coil a voltage which is proportional to the rate of change of the magnetic flux. A uniform tooth structure corresponds to a voltage profile which is similar to a sinusoid, so that the wheel rotation speed can be obtained from the interval between the zero crossings of the induction voltage. The amplitude of the voltage signal additionally is proportional to the rotation speed.
Such a known inductive wheel rotation speed sensor system is frequently used in wheel slip control systems, such as anti-lock braking systems and drive slip controllers. A further design for a sensor which is sensitive to magnetic fields and is suitable, for example, for position determination on a shock absorber of a vehicle, is described in European Patent document EP O 242 058 A1. The sensor disclosed there is controlled by a microcomputer and contains an excitation coil as well as a sampling coil. The sampled signal of the sampling coil is dependent on the shock absorber position and can be evaluated by the microcomputer.
A test of the serviceability of a vehicle which is equipped with such a wheel rotation speed sensor system requires, inter alia, the checking of the controllers which process the wheel rotation speed and other vehicle components which react to the wheel rotation speed sensor signals, as well as their connections to one another. This test can be carried out in a known manner on a conventional roller test rig which is of complex design and is not transportable. For this purpose, the motor vehicle is accelerated on the roller test rig to the predetermined rotation speed levels, and the inductive rotation speed sensors on the wheels provide a signal which is proportional to the rotation speed. The signal is passed on to the relevant vehicle components to be tested. This tests, for example, whether the windscreen wiper interval changing, which is dependent on rotation speed, is operating; whether the tachometer is correctly calibrated; whether the safety turn-off of a cruise controller is responding in the desired manner; and/or whether existing longitudinal dynamics controllers are providing appropriate values. It is possible to provide a test computer in order to evaluate the diagnostic information. Very high wheel rotation speeds are necessary for some of these tests, for which the conventional test rig must be designed if it is intended to be used to carry out such tests. Transportable test rigs, such as the mini-brake test rig which is disclosed in Laid-Open Specification DT 25 45 414 A1, are also already known in addition to fixed-position roller test rigs.
It is furthermore known to perform tests of vehicle components using simulation and/or stimulation apparatuses. For example, Great Britain Patent document GB 2 096 327 A discloses a portable test device in which it is possible to test the serviceability of tachographs as well as of the pulsed signal lines which lead to associated sensors. The test device is looped into the connection path between the tachograph and the sensors for this purpose. The test device allows signals to be produced which simulate sensor signals which are dependent on the wheel rotation speed, in order to check the tachograph, and allows a test voltage to be produced for testing the connecting lines to the sensors for short circuits or interruptions, and also allows the corresponding response signals to be evaluated.
German Patent document DE 3 936 988 A1 describes an apparatus for motor vehicle diagnosis, in which a diagnostic signal coupler can include a stimulation unit for stimulation of a signal destination, such as an actuator. It is possible for the stimulation signal to be transmitted in a DC-isolated manner via transformers or optocouplers. The arrangement of a stimulation unit within a vehicle test device is also known, from European Patent document EP O 47 813 B1. This specifies the provision of the stimulation apparatus for simulation of signals when the vehicle is stationary in the same way as those which actually occur during operation of the vehicle in order, in this manner, to test associated signal processing components in the vehicle, with the vehicle stationary, such as electronic fuel injection systems, electronic ignition systems or automatic brake systems, for example.
European Patent document EP O 338 373 A3 discloses a test ring for testing the drive train of a vehicle, in which a plurality of electrical load machines, whose torque is independently controlled, are connected via flanges directly to the shafts of the drive train to be tested, instead of the conventional rollers. The load machines are driven by a simulation computer. In this manner, the drag during motion, the wheels, and the vehicle acceleration behavior, are simulated by actual vehicle components, such as the main drive train, the axle drive, shafts, the clutch, the transmission and the internal combustion engine. At the same time, simulations of turning, of spinning wheels, of different wheel radii, and of spinning or locked wheels are possible.
There is therefore needed a device for testing vehicle components which receive signals from a wheel rotation speed sensor system which is sensitive to magnetic fields. By using this device, complex test processes for these components can be carried out flexibly and reliably with little design complexity.
These needs are met according to the present invention by a test device for vehicles having a wheel rotation speed sensor which is sensitive to magnetic fields. An appliance for simulation of wheel rotations has a magnet coil which stimulates sensors and can be positioned in the magnetic field region of the sensor such that magnetic field coupling is provided. A control unit applies an AC voltage to the magnet coil. The frequency of the AC voltage determines the sensed rotation speed of the simulated wheel rotation.
The provision of the appliance which simulates wheel rotation and whose design is optimally matched to the stimulation of an inductive wheel rotation speed sensor while keeping the design complexity low, makes it possible to check vehicle components to which such rotation speed sensor signals are fed. This testing can be done when the vehicle is stationary and without actual wheel rotation having to be carried out. To this end, the control unit uses the magnet coil to simulate the reaction signal for the sensor receiving part as is supplied, for example, by a coupled toothed wheel, which influences magnetic fields during actual wheel rotation.
It is an advantage of the invention that wheel rotation speed profiles of predetermined driving cycles can be simulated by the computer for the wheel rotation speed sensor system, so that vehicle components which are sensitive to wheel rotation speeds can be tested in the conditions of a desired driving cycle when the vehicle is, in reality, stationary.
A further advantage of the invention is that the test device additionally has rollers which are driven by DC motors and can be brought into rolling contact with a vehicle wheel in order to be able to carry out actual rotations of selected wheels for specific tests. Comparatively slow wheel speeds are sufficient for these tests of, for example, mechanical, hydraulic or pneumatic vehicle components such as ABS or wheel-slip traction control brake system components. In view of this, in contrast to complex, stationary roller test rigs, the roller unit does not need to be designed for high speeds and loads and, can be constructed in a compact and/or transportable manner.
In combination with the device which simulates wheel rotations, functional tests can be carried out with only simulated wheel rotation, for example for cruise control testing. This is done with wheel rotations which are actual and free of engine load. In addition, the wheel rotations are simulated if required, for example for ABS or wheel-slip traction control testing. The tests can also be done with actual wheel rotations under engine load and, if required, additional simulated wheel rotations on non-driven axles, for example for testing the electronic transmission control. Furthermore, this refinement makes it possible to avoid the consequent double fault in brake system testing, in particular for testing vehicle dynamics control.
Until now, the connections of the rotation speed sensors and of the ABS brake system have been tested on the conventional roller test rig. For this purpose, the wheels are accelerated by the vehicle drive, the non-driven wheels are also accelerated via a belt coupling on the roller test rig, and the belt drive is subsequently decoupled. The wheels are sequentially braked via the ABS. The sequential braking is introduced via the diagnostic interface and the drop in rotation speed of the driven wheels is measured. If the left-hand and the right-hand sensor connection and, in addition, the left-hand and the right-hand ABS control section, for example, have now been interchanged during assembly, this fault cannot at the moment be detected. The vehicle dynamics control, which makes use of the sensor system and the ABS, can thus not be completely tested.
This double fault can, by contrast, be detected easily using the test device designed according to the present invention. For this purpose, the sensors are stimulated and the stimulation values are read out via the diagnostic interface or via a data bus. The comparison of the values which have been read out with the stimulation values indicates whether the sensors are correctly connected. The further testing of the ABS is carried out using the roller unit. The above double fault can thus be unambiguously detected.
In addition, this refinement of the invention allows the detection of double faults in the system, for example if the transmission controller contains an incorrect software version with incorrect gear ratios and, at the same time, an axle which is intrinsically not correct for the vehicle but whose gear ratio matches that of the controller has been installed. Using conventional means, this double fault can only be detected at high cost. By contrast, using the test device which has been developed according to the invention, the connection and the software of the controller can initially be determined via a diagnostic line using a wheel rotation simulation with associated wheel rotation speed sensor stimulation and, subsequently, the gear changes can be tested by actually driving the wheels on the drive axle. Advantageous implementations of the roller unit are also provided.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.